Ž . European Journal of Pharmacology 351 1998 R1–R3 Rapid communication Microtubule disruption potentiates phenylephrine-induced vasoconstriction in rat mesenteric arterial bed Romulo Leite ) , R. Clinton Webb Department of Physiology, 7813 Medical Sciences Building II, UniÕersity of Michigan Medical School, Ann Arbor, MI 48109-0622, USA Received 6 May 1998; accepted 8 May 1998 Abstract The pressor response induced by phenylephrine in the rat isolated mesenteric arterial bed was significantly increased following Ž . treatment with nocodazole, a drug that disassembles microtubules 10 mM, 90 min . This increase was even greater in the presence of Ž . Ž . nitric oxide NO synthase inhibition, and completely reversed by paclitaxel 20 mM , a stabilizer of microtubules. These results demonstrate that disassembly of microtubules enhances vasoconstriction to receptor activation, suggesting that the microtubules modulate the transduction of intracellular signals in endothelium and vascular smooth muscle cells. q 1998 Elsevier Science B.V. All rights reserved. Keywords: Microtubule; Blood vessel; Nocodazole Cytoplasmic microtubules serve as a network by which vesicles and membrane-bound organelles can travel. In addition, microtubules regulate cell shape and movement Ž and participate in several cell signaling events PeMan et . al., 1983; Rowinsky et al., 1990 . Disruption of micro- tubules induces shortening in cultured cells and potentiates agonist-induced contraction in isolated pulmonary arteries Ž . from rats Sheridan et al., 1996 . In this study we tested the hypothesis that microtubules oppose contraction in- duced by receptor activation. Mesenteric arterial beds from normotensive Sprague– Dawley rats were perfused at 2.5 mlrmin with a modified Ž . Krebs solution 378C and pH 7.4 and the perfusion pres- sure was continuously monitored. A dose-response curve Ž . to phenylephrine 1.56–400 nmol was performed after a 30 min stabilization period, followed by incubation with either an inhibitor of microtubular assembly, nocodazale Ž . Ž . 10 m M , or vehicle dimethyl sulfoxide, DMSO . After a 90 min incubation period another dose-response curve was again established. The same protocol was repeated in the v Ž . presence of N -nitro-L-arginine L-NNA, 300 m M , an Ž . inhibitor of nitric oxide NO synthase, alone or combined Ž . with the microtubule stabilizer paclitaxel 20 m M. ) Corresponding author. Tel.: q1-734-763-5606; fax: q1-734-647- 7950; e-mail: rlicbfar@mono.icb.ufmg.br The pressor response induced by phenylephrine was significantly potentiated in the presence of nocadazole Ž . ED 101.3 vs. 79.8 nmol, Fig. 1A and D . Treatment 50 with L-NNA caused a significant left shift of the dose–re- sponse curve induced by phenylephrine. The presence of nocodazole in the L-NNA treated vessels induced a further Ž . potentiation ED 17.6 vs. 4.5 nmol, Fig. 1B and D . This 50 effect induced by nocodazole was completely blocked by Ž . paclitaxel ED 13.8 vs. 12.0 nmol, Fig. 1C and D . 50 Phenylephrine elicits intracellular responses by activat- ing receptors linked to G -mediated stimulation of phos- a pholipase C which hydrolyzes the lipid precursor phos- Ž . phatidyilinositol 4,5-biphosphate PIP to generate second 2 messengers, diacylglycerol and inositol 1,4,5-triphosphate Ž . IP . Diacylglycerol and IP trigger a variety of cellular 3 3 functions by activating protein kinase C and mobilizing Ž . stored calcium Malarkey et al., 1996 . Ž . It has been suggested Popova et al., 1997 that the activity of phospholipase C is regulated through the inter- action of tubulin, a cytoskeletal protein that constitutes the microtubules, with a specific G protein a subunit or with the phospholipase C substrate PIP . 2 Ž . Kolodney and Elson 1995 have shown that disruption of microtubules increases phosphorylation of the myosin Ž . regulatory light chain LC in cultured fibroblasts. This 20 effect could be explained by an increased activity of myosin light chain kinase or a reduced activity of myosin 0014-2999r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved.